L-Trimethylsilyl-2-butyne

Methyl-l-(trimethylsilyl)allene (90% purity, contaminated with 10% 1-trimethylsilyl-l-butyne) was prepared by the method of Danheiser, R. L. Tsai, Y, M. Fink, D. H. Org. Synth, 1988, 66, 1. 

When chlorotrimethylsUane [(013)3810] is treated with lithium azide (UN3) in oxacyclopentane (THF), trimethylsilylazide [(CH3)3SiN3] results. Treatment of the latter with 2-butyne (dimethylacetylene, CH3C=CCH3) results in a cycloaddition reaction (Scheme 10.64), and, what is of particular interest, the 1-trimethylsilyl-l,23-triazole that results undergoes a 1,5-sigmatropic rearrangement to generate the more stable 2-trimethylsilyl-l, 2,5-triazole. 

The reaction of 1-21 with alkynes is regioselective. When unsymmetrical alkynes such as 1-phenyl-1-butyne was used, l-43a and l-44a both as single regioisomers were isolated upon hydrolysis of reaction mixture at 50 °C and 90 °C respectively. The Ph group was selectively located at a-position of CpaZr moiety. The substituents on alkynes also have an effect on the chemoselectivity of the reaction. When 1-trimethylsilyl-l-propyne was used, only zirconacyclopentadiene l-43b was isolated regioselectively, and the corresponding zirconacyclohexadiene complex was not isolated (Scheme 1.21) [47, 48]. 

With telluronium salt (d) (typical procedure) A solntxon of n-BuLi (1.5 mmol) in hexane is added to a solution of the telluronium salt (0.65 g, 1.5 mmol) in dry THF (10 mL) at -78°C under N2. After 30 min, a solution of p-chlorobenzaldehyde (0.168 g, 1.2 mmol) in THF (2 mL) is added dropwise at -78°C and the reaction mixture is allowed to warm at room temperature. After the reaction is complete (monitored by TLC), H2O (1 mL) is added and the solution is stirred for another 1 h. The mixture is then extracted with ether (3x5 mL). The combined extracts are washed with brine, dried (Na2S04), filtered and concentrated under vacuum. Flash chromatography on an SiOj column gives l-(p-chlorophenyl)-4-(trimethylsilyl)-3-butyn-l-ol (0.265 g (87%) (98% GC purity)). 

Trimethylsilyl-1-butyne, 218 l-Trimethylsilyl-2-butyne, 329 Trimethylsilyl chlorochromate, 327 Trimethylsilyldiazomethane, 327 p-Trimethylsilylethanesulfonyl chloride, 328... 

Trimethylsilyl-4-bromomagnesio-l-butyne (activation of magnesium by dry stirring) [38]... 

Under similar conditions phenylacetvlene. 1-hexyne. 3.3-dimethyl-l-butyne. and trimethylsi-lylacetylene give f )-l-phenyl-1-pen ten-3-one, ( )-4-nonen-3-one, (Fj-6.6-dimethyl-4-hepten-3-one, and ( )-l-trimethylsilyl-l-penten-3-one in 76, 68, 93, and 62% yields, respectively5. Thus, the reaction of terminal acetylenes proceeds with high stereo- and regioselectivity. The propionyl group is introduced at the less sterically hindered acetylenic carbon atom. These reactions arc assumed to include /i-acylvinylrhodinm complexes as the common key intermediates. 

In a similar manner, allenylborane derived from 3-(tert-butyldimethylsilyl)-l-(trimethylsilyl)-propyne gives mainly (lS,2i )-2-(fert-butyldimethylsilyl)-l-[2-(3-methyl-3-buten-l-ynyl)-l-cyclopentenyl]-4-(trimethylsilyl)-3-butyn-l-ol (54%) and (lS,2i )-2-(ferf-butyldimethylsilyl)-l-[2-l-cyclohexenylethynyl)-l-cyclopentenyl]-4-(trimethyl silyl)-3-butyn-l-ol (55%) (Chart 6.17) [1]. 

Purification allenes (la), (lb), and (Ic) are purified by distillation at reduced pressure or by column chromatography. Allene (Id) is distilled at atmospheric pressure. The allenyl-silanes obtained by the Vermeer method typically contain up to 7-8% of the trialkylsilyl-l-butyne isomer produced by Sn2 reaction. This mixture can be used directly in most subsequent reactions without further purification. If desired, however, the alkynyl contaminant can be selectively removed by treatment of the mixture with silver(I) nitrate in (10 1) methanol-water at room temperature for one hour. 1-Methyl-l-(trimethylsilyl)-allene is obtained in 79% yield after pentane extraction and distillation. 

In the presence of CO, the Pd(PhCN)2Cl2-catalyzed cyclization of 1,1-disubstituted 4-(trimethylsilyl)-3-butyn-l-ols produces y-butyrolactones (eqs 73 and 74).4 ... 

Magnesium turnings (1.27 g, 52 mmol) are stirred in an argon atmosphere for 48 h in a 100 ml three-necked round-bottomed flask [12], Dry THF (20 ml) is added, followed dropwise by a solution of 4-bromo-l-trimethylsilyl-1-butyne (2.56 g, 12.5 mmol) in dry THF (20 ml). After the initial exothermic reaction has subsided, the mixture is stirred at room temperature for 1 h. 

Palladium(ll)-catalyzed intramolecular stereoselective Irons alkoxycarbonylation of 4-alkyl- and 4-aryl-3-butyn-l-ols 7 gives /f-tetrasubstituted a-methylene-y-butyrolactones 8 if conducted in the presence of copper(II) chloride, methyloxirane and triethyl orthoacetate. In the absence of the copper salt, intramolecular dicarbonylation occurs (e.g., giving 9, see Section 1.5.8.3.3.). The latter reaction type is also observed if the alkyne moiety is substituted by a trimethylsilyl instead of an alkyl or aryl group60,61. 

Reduction of the lactone 137 to the corresponding lactol 138 necessitated use of DIBAL quenching the reaction with methanol followed by workup with aqueous potassium sodium tartarate furnished the product as a clear viscous oil that solidified on standing to a white solid. The anomeric hydroxyl group was conveniently protected by the formation of terf-butyldimethylsilyl ether by treatment with rert-butyldimeth-ylsilyl chloride, imidazole, and A,A-dimethylaminopyridine. Further activation of the anomeric position in compound 139 with trimethylsilyl bronfide followed by treatment with l-t-butyldimethysiloxy-3-butyne and n-butyUithium yielded a transicis mixture (1 1) (140) that was used without further purification. Reaction of compound 140 with tetrabutylammonium fluoride led to deprotection of the hydroxy functionality. The resulting transicis mixture of the alkynols was subjected to extensive chromatography and repeated crystallization to obtain a tran -alcohol (141) as a white crystalline solid. Further elaboration to 131 was carried out by appropriate modifications of a literature procedure. ... 

As model compounds we have chosen (3-hydroxy-l-propenyl)tris(trimethylsilyl)silanes (4a-c), which were obtained by AIBN-initiated additions of tris(trimethylsilyl)silane (3) to propargylic alcohol, 2-methyl-3-butyn-2-ol and l,l-diphenyl-2-propyn-l-ol, respectively (Eq. 1). In agreement with literature data [3], in the case of the reaction of 3 with propargylic alcohol the Z-olefin 4a was obtained. NMR studies of 4b and 4c revealed an E-configuration for the two olefins. 

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